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United States Patent |
6,050,215
|
Koulik
,   et al.
|
April 18, 2000
|
Plasma stream generator with a closed configuration arc
Abstract
A plasma stream generator with a closed-configuration arc for achieving a
stream comprising a central area at a uniform or very low temperature. The
generator comprises a higher or even much higher number of electrode pairs
than is usual, whereby rows may be formed and, in particular, an elongate
stream, i.e. a curtain, may be achieved. The orientation problems
resulting from the closeness of the jets and the increased
attraction/repulsion therebetween are solved by means of magnetic devices
(coils) of which there are generally three for a pair of electrode
chambers.
Inventors:
|
Koulik; Pavel (Yverdon-les-Bains, CH);
Konavko; Rudolph (Yverdon-les-Bains, CH);
Saishenko; Anatolii (Yverdon-les-Bains, CH);
Samsonov; Mikhail (Yverdon-les-Bains, CH)
|
Assignee:
|
IST Instant Surface Technology S.A. (CH)
|
Appl. No.:
|
068415 |
Filed:
|
September 8, 1998 |
PCT Filed:
|
November 12, 1996
|
PCT NO:
|
PCT/CH96/00403
|
371 Date:
|
September 8, 1998
|
102(e) Date:
|
September 8, 1998
|
PCT PUB.NO.:
|
WO97/18693 |
PCT PUB. Date:
|
May 22, 1997 |
Foreign Application Priority Data
Current U.S. Class: |
118/723R; 219/121.47; 219/121.5; 310/11 |
Intern'l Class: |
H05H 001/44 |
Field of Search: |
310/11
219/121 PR
|
References Cited
U.S. Patent Documents
3940641 | Feb., 1976 | Dooley | 310/11.
|
4275287 | Jun., 1981 | Hiratake | 219/121.
|
Primary Examiner: Breneman; Bruce
Assistant Examiner: Zervigon; Rudy
Attorney, Agent or Firm: Browning; Clifford W.
Woodard, Emhardt, Naughton Moriarty & McNett
Claims
We claim:
1. Plasma arc stream generator, of closed configuration, comprising
electrode chambers working in pairs, each pair having an anode and a
cathode and being connected to a DC power source, the plasma jets having
current passing through them, with spatial orientation by means of an
external magnetic field directed such that the plasma jets from the
chambers converge and form a common plasma stream with a central zone of
uniform or lowered temperature, characterised in that the generator
comprises at least three pairs of electrode chambers as above, and the
said chambers are arranged in relation to each other such that the
assembly is symmetrical without all the chambers being positioned in the
same circle, and in that said generator further comprises one or more
magnetic orientation devices (of the jets) outside all the electrode
chambers, the generator creating a common plasma stream of closed
configuration, elongated in shape with a central zone of uniform or
lowered temperature in relation to the peripheral zone resulting from the
convergence of at least six plasma jets.
2. Generator according to claim 1, characterised in that the magnetic
device dictating the orientation of the plasma jets consist, for each
electrode chamber, of three sections of magnetic conductor, two of which
being positioned perpendicular to the plasma jets and the third between
the plasma jets.
3. Generator according to claim 1, characterised in that the electrode
chambers are arranged in two groups.
4. Generator according to claim 3, characterised in that the two groups of
chambers are arranged in parallel rows.
5. Generator according to claim 4, characterised in that the rows are
straight.
6. Generator according to claim 5, characterised in that the electrodes in
one and the same group or the same row of chambers respectively are all of
the same polarity.
7. Generator according to claim 5, characterised in that one and the same
group or same row of chambers respectively contains electrodes of opposite
polarities.
8. Generator according to claim 7, characterised in that the electrodes in
the same group or same row are arranged such that the polarities are
alternated, at least partially.
9. Generator according to claim 5, characterised in that the electrode
chambers in the same group, or same row respectively, are constructed in a
single, continuous block.
10. Generator according to claim 1, characterised in that the electrodes in
one and the same group or the same row of chambers respectively are all of
the same polarity.
11. Generator according to claim 1, characterised in that one and the same
group or same row of chambers respectively contains electrodes of opposite
polarities.
12. Generator according to claim 11, characterised in that the electrodes
in the same group or same row are arranged such that the polarities are
alternated, at least partially.
13. Generator according to claim 1, characterised in that the electrode
chambers in the same group, or same row respectively, are constructed in a
single, continuous block.
Description
This invention concerns a plasma arc stream generator with a closed
configuration.
Plasma technology, and in particular devices for creating a stream of
closed configuration may be used in surface treatment processes
(sterilization, cleaning, etching, modifying, deposit of coatings and
films) of monolithic and disperse materials, and for obtaining and
treating chemical products, in electronics, the automotive industry,
metallurgy, the chemical and food industry, medicine and many other
sectors.
This type of device for generating a plasma arc stream of closed
configuration with a central zone of uniform or lowered temperature is
already known. This device is illustrated in the document entitled <<Basis
for execution of a dynamic plasma treatment method for solid surfaces>>,
by P. P. Koulik et al, <<Plasmokhimia 1987", Moscow 1987, part 2, pp. 58
to 96.
The abovementioned document describes a device containing two pairs of
electrode chambers (cathodes and anodes) connected in pairs to DC power
sources. The parameters of the plasma channels of the electrode chambers
(cathodes and anodes) correspond to the data published in the document
entitled <<Twin-jet plasmatron>>, Genbaiev G. G. and Enguelsht V. S.,
Frounze 1983.
When the electrode chambers are energized, two arcs are activated and form
four plasma jets with the current passing through them. The spatial
orientation of the plasma jets is obtained by external magnetic fields
directed in relation to the electrode chambers such that the plasma jets
from the electrode chambers converge and form a common stream of axially
symmetrical plasma, with the current passing through (plasma funnel) whose
section, perpendicular to the axis of symmetry of the stream, has a
unifrom or lowered temperature zone in relation to the peripheral part of
the stream.
It is into this zone that the gaseous, disperse or solid state components
are injected via one or more concentric axial channels into the plasma
funnel for conversion before use.
The advantage of this known type of plasma generator lies in the special
configuration of the plasma stream. In fact, this is in the form of a
plasma funnel, enabling the introduction and treatment (processing) by the
plasma of different products in different forms (gaseous, liquid or
solid), and use of this generator for high performance surface
sterilization, cleaning, etching, modifying and also coating with films.
The disadvantage of the generator of the above type is that the plasma
stream is always of reduced dimensions, dictated by the diameter of the
resultant plasma stream. However, there are numerous applications for
which a larger sized plasma stream would be useful, provided of course
that the closed configuration of the stream is maintained, as this affords
a central zone of uniform or lowered temperature.
The purpose of this invention is to offer a plasma arc stream generator of
closed configuration, whose section, perpendicular to the direction of the
stream, is elongated in form (plasma curtain) affording a central zone of
uniform or lowered temperature.
To this effect, the invention concerns a plasma arc stream generator of
closed configuration, comprising electrode chambers working in pairs, each
pair having an anode and a cathode and being connected to a DC source,
with the current passing through the plasma jets generated, whose spatial
orientation is obtained by means of an external magnetic field directed
such that the plasma jets from the chambers converge and form a common
plasma stream with a central zone of uniform or lowered temperature, the
said generator comprising at least three pairs of electrode chambers as
above, with the said chambers positioned in relation to each other so that
the assembly is symmetrical without, however, the chambers being
positioned on the same circle.
According to one embodiment, the generator further comprises one or more
magnetic orientation devices (for the jets) outside all the electrode
chambers, the generator creating a common plasma stream of closed
configuration, elongated in shape with a central zone of uniform or
lowered temperature in relation to the peripheral zone resulting from
convergence of at least six plasma jets.
The magnetic device dictating the orientation of the plasma jets may
consist, for each electrode chamber, of three sections of magnetic
conductor, two of which are positioned perpendicular to the plasma jets
and the third between the plasma jets.
The electrode chambers may be positioned in two groups, the two groups of
chambers possibly being arranged in parallel rows, the rows possibly being
straight.
According to one variant, the electrodes in one and the same group,
respectively in one and the same row, of chambers are all of the same
polarity, the electrode chambers of one and the same group or same row
respectively possibly being constructed in a single, continuous block.
According to another variant, one and the same group, or same row
respectively, of chambers contains electrodes of opposite polarity, the
electrodes in any one group or row being positioned such that they are of
alternating polarities, at least partially.
The solution proposed in this invention basically consists in equipping the
generator with at least one pair of electrode chambers (anodes and
cathodes) in addition to of the generator known from the <<Koulik>>
document referred to above.
A description is given below of the generator according to the invention,
based on the drawing in which:
FIG. 1 shows the generator according to the invention, constructed such
that the electrode chambers are arranged in two parallel straight lines;
the references in FIG. 1 are as follows:
1. Electrode chambers
2. Plasma jets
3. Resulting plasma stream
4. Plasma stream zone of lowered temperature
5. Magnetic conductors with winding coils
FIG. 2 shows an electrode chamber in the form of a relatively narrow
parallelepiped according to the invention, and more particularly the
following details: FIG. 2a--general arrangement, FIGS. 2b to 2d--sections;
the references relating to FIG. 2 are as follows:
1. Plasma jet
2. Electrode
3. Diaphragm
4. Dielectric seal
5. Current channel
6. Water cooling ducts
7. Electric power supply cable
FIG. 3 is a diagrammatic view showing the orientation of the plasma jet
magnetic control device, in the plane of the jets, according to the
invention; the references relating to FIG. 3 are as follows:
1. Electrode chamber (anode, cathode)
2. Plasma jets
3. Magnetic conductor
4. Winding coils
5. Magnetic lines
Looking at FIG. 1, it will be noted that the electrode chambers are
connected in pairs (consisting of an anode with a cathode) to current
sources. The proposed plasma generator comprises at least six electrode
chambers generating six plasma jets with the current passing through them.
The orientation of the electrode chambers is designed to create a plasma
curtain and not, as in the prior art design, to merely form a plasma
funnel. As in the <<Koulik>> document referred to above, firstly the
orientation of the resulting plasma stream and secondly determination of
the shape of the stream are dictated by means of external magnetic fields.
These magnetic fields are directed in relation to the electrode chambers
such that the plasma streams emerging from the electrode chambers form a
common plasma stream that is symmetrical in relation to a given surface,
with the currents from the electrode chambers passing through (plasma
curtain).
Different arrangements of the electrode chambers are possible along
surfaces of different symmetry; cone of circular or elliptical section,
parallel planes, single planes, etc. Depending on this arrangement,
different plasma stream configurations can be obtained that can be adapted
to suit different practical solutions, and hence different applications.
The arrangement which warrants closest attention is that in which the
electrode chambers are positioned in two parallel lines, situated in two
planes which intersect. In this case, a single plasma stream is fomed,
obtained by the convergence of the initial plasma jet zones from the
electrode chambers, whose temperature is high, and the plasma stream
resulting in a flat curtain affording a zone of uniform or lowered
temperature in its centre.
The arrangement of the electrode chambers in two rows can be determined
such that in each row the anode and cathode chambers alternate, or the
electrodes in any one row are all of the same type, i.e. all needs or all
cathodes.
The channels of the electrode chambers through which the current passes
consist of copper diaphragms with dielectric seals. The electrodes
themselves (copper anode, tungsten cathode) are positioned at the entry to
the current channels. All the parts in the electrode chambers are
water-cooled. The gas forming the plasma passes through the current
channels. The diameter of the electrodes and the diaphragms, and the
thickness and number of these, is optimised to obtain plasma jets of high
stability.
The spatial orientation of the plasma jets is controlled by magnetic field.
This orientation control is designed to force the plasma jets to remain in
the direction dictated by the current channel.
Under the action of their particular magnetic fileds, the plasma jets
mutually repel each other when they are of opposite polarity, and attract
in the reverse case.
When the electrode chambers are of the same polarity in a row, the mutual
attraction of the jets (in the absence of external magnetic fields) means
that the plasma jets at the ends of the row have a substantial inclination
to the centre of the row. The external magnetic field, i.e. the control
referred to above, should this in case counteract this attraction and
re-establish the direction of the plasma jets dictated by the current
channel.
If the polarities of the jets in the same line alternate, the plasma jets
repel each other, causing a change in distance between the different jets
downstream of the electrode chambers, or inevitable slight differences in
gas flowrate and current between the various plasma jets.
The application of external magnetic fields enables achievement of the
required orientation characteristics of the plasma jets and to a large
extent corrects the effects due to their proximity. At any event, the
magnetic force should be orientated in the plane of the plasma jets,
perpendicular to their direction of flow.
Looking at FIG. 3, the magnetic device for control of the jets can be seen,
which, in the plane of the jets, contains three sectors of magnetic
conductors with winding coils. The direction of the current in the coils
is consistent with the direction of action on the plasma jets.
The size of the field can be selected individually for each plasma jet by
varying the current in the coils. The magnetic device is installed
separtely for each pair of electrode chambers (anode and cathode). The
magnetic conductor situated between the plasma jets may coincide with the
system for introducing the chemical product or treated product into the
plasma curtain.
The arrangment of the chambers in rows, with alternating polarity in the
row, simplifies magnetic control as the jets with the current passing
through partially compensate the specific magnetic field (with the
exception of the end jets).
Nonetheless, in view of the risk of short-circuit between chambers of
different polarity, the distance between them should ensure that any such
short-circuit is ruled out. This means increasing the distance between the
plasma jets and moving their point of convergence towards the areas of
lowest temperature.
The arrangement of the chambers in rows, with the same polarity for the
entire row, requires more intense action on the jets by the external
magnetic fields (especially on the end jets). However, the advantages of
this arrangement is that the electrode chambers can be positioned one
against the other, which reduces the distance between the jets and means
that their point of confluence can be positioned in the high temperature
zone of the plasma. In addition, it is possible in this case to have the
electrode chambers in a single block and the diaphragms in a single unit.
This also means a reduction in distance between the jets.
In a more precise embodiment, the electrode chambers are 2 cm wide and
positioned one after the other. They are thus arranged in two parallel
straight lines of constant polarity. The generator consists of 50 pairs of
electrode chambers. The current passing in each pair of chambers is 50 A,
the voltage is 100 V, the power factor of each jet being 5 kW, with a gas
heat output of 50%.
The plasma curtain, downstream of the confluence point of the jets, has a
total length of 1 m, a width of 1 cm and a total power factor of 125 kW.
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